package chapter2;

import chapter1.InstallBouncyCastle;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

/**
 * Symmetric encryption example with padding and CBC using DES
 * with the initialization vector inline.
 */
public class InlineIvCBCExample extends InstallBouncyCastle {
    public static void main(String[] args) throws Exception {
        byte[] input = new byte[]{
                0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
                0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
                0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07};
        byte[] keyBytes = new byte[]{
                0x01, 0x23, 0x45, 0x67, (byte) 0x89, (byte) 0xab, (byte) 0xcd, (byte) 0xef};
        byte[] ivBytes = new byte[]{
                0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01, 0x00};

        SecretKeySpec key = new SecretKeySpec(keyBytes, "DES");
        IvParameterSpec ivSpec = new IvParameterSpec(new byte[8]);
        Cipher cipher = Cipher.getInstance("DES/CBC/PKCS7Padding", "BC");


        System.out.println("input : " + Utils.toHex(input));

        // encryption pass

        cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);

        byte[] cipherText = new byte[cipher.getOutputSize(ivBytes.length + input.length)];

        int ctLength = cipher.update(ivBytes, 0, ivBytes.length, cipherText, 0);

        ctLength += cipher.update(input, 0, input.length, cipherText, ctLength);

        ctLength += cipher.doFinal(cipherText, ctLength);

        System.out.println("cipher: " + Utils.toHex(cipherText, ctLength) + " bytes: " + ctLength);

        // decryption pass

        cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);

        byte[] buf = new byte[cipher.getOutputSize(ctLength)];

        int bufLength = cipher.update(cipherText, 0, ctLength, buf, 0);

        bufLength += cipher.doFinal(buf, bufLength);

        // remove the iv from the start of the message

        byte[] plainText = new byte[bufLength - ivBytes.length];

        System.arraycopy(buf, ivBytes.length, plainText, 0, plainText.length);

        System.out.println("plain : " + Utils.toHex(plainText, plainText.length) + " bytes: " + plainText.length);
    }
}
